The invention relates to a pipette for gripping components by means of a vacuum, in particular when mounting components on printed circuit boards.
A pipette of this nature is known, for example, from German utility mode 94 06 244. According to this document, the pipette has a suction opening on its end surface or side which faces toward the component. The component can be sucked onto a bearing surface, which surrounds the suction opening, of the end side. The bearing surface forms part of an elastomeric bearing member which is inserted into the end side of a base body of the pipette and which projects slightly beyond the end side. The bearing member is designed as an O-ring which bears with a press fit against the inner wall of the base body. The O-ring improves the suction ability of the pipette, since it rests more securely against the surface of the component which has been sucked on than does a hard component.
Mounting of components on printed circuit boards increasingly involves the use of mounting machines which have a movable revolver head which accommodates, stores and transports the components, rotates them to their desired installation position, adjusts their position and deposits them on the printed circuit board. The various movement operations result in accelerations which are such that there is a risk of the position of the component changing with respect to the pipette. However the permissible position deviation is so small that such a change in position must be avoided at all costs. In particular, it is also necessary to keep the suction distance between the pipette and the component within tight tolerances, in order to allow the components to be picked up and set down without them being subject to shocks.
The deformability of the known O-ring is so high that such levels of accuracy cannot be reliably achieved. In particular, the centrifugal force of the components which have been sucked on in the radial direction, which force occurs when the revolver head rotates, may result in the O-ring, which has been pressed, becoming detached.